1. Field of the Invention
The present invention relates to acoustic signal generation systems. More particularly, the present invention relates to a variable reluctance acoustic projector for use in underwater sonar applications.
2. Description of Related Art
Variable reluctance transducers (VRT) represent one of several technologies used to generate acoustic signals in surveillance and tactical sonar arrays. A variable reluctance transducer typically includes an electromagnetic device having a movable core mounted in a housing opposite a substantially fixed core. In response to excitation of the fixed core via coil windings, the movable core is deflected, actuating a projector diaphragm to generate an acoustic signal.
When variable reluctance transducers are used to actuate an acoustic projector for sonar applications, it is necessary to ensure both precise alignment of opposing electromagnetic cores and rigid attachment of one or both cores to portions of the water tight housing containing the cores. Precise alignment of the electromagnetic cores is important for two reasons.
First, the electrical inductance of the projector varies with the width of the air gap between the opposing cores. If air gap dimensions fall out of tolerance due to core misalignment, the resulting variance in the air gap, which may amount to a significant percentage of the nominal uniform air gap thickness, can cause the actual electrical response characteristic of the electromagnetic transducer to substantially differ from the desired response.
Second, core misalignment may produce an actuation thrust vector that does not coincide with the acoustic axis of the projector, resulting in a distorted beam pattern. This condition may occur if the pole faces of opposing cores are not sufficiently parallel, or if they are shifted horizontally relative to one other. In such a case, unwanted signal harmonics may be produced.
Rigid attachment of the cores to the housing is necessary to avoid undesirable shunting of acoustic energy away from the outgoing acoustic beam. Furthermore, both precise core alignment and rigid attachment must be maintained for stringent dynamic operation conditions to enable the sonar transducer to withstand explosive shock specifications.
Existing VRT structures fail to provide adequate alignment and sufficiently rigid attachment of the electromagnetic cores within the acoustic projector housing. As a result, conventional VRT sonar arrays are susceptible to the problems discussed above.